<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>扇形</title>
    <style>
        .sector{
            width: 0;
            height: 0;
            border: solid 100px;
            border-color:red transparent transparent transparent ;
            border-radius: 100px;
        }
    </style>
</head>
<body>
    <div class="sector"></div>
</body>
</html>